Low-ohmic electrical resistance



Sept. 18, 1951 A. WlRK 2,568,600

LOW-OHMIC ELECTRICAL RESISTANCE Filed Aug. 12, 1950 Inventor Mdo a zr/z.

Patented Sept. 18, 1951 LOW-OHMIC ELECTRICAL RESISTANCE Adolf Wirk,Berlin-Spandau, Germany, assignor to Siemens & Halske,Aktiengesellschaft, Siemensstadt, near Berlin, Germany, a corporation ofGermany Application August 12, 1950, Serial No. 179,068

In Germany August 19, 1949 9 Claims.

This invention is concerned with low-ohmic electrical resistances whichhave within the range of short waves a substantially constant,substantially phase-free resistance value.

A brief review of the prior art is rendered below in order to supportthe understanding of the invention.

Laminated resistances are known, comprising a tubular insulating membercovered, for example, with a carbon resistance layer. While suchresistances are, within a certain range, nearly independent of thefrequency, their resistance values are for some purposes too high.Attempts to reduce the resistance value by proper proportioning of theresistance layer failed because it is diflicult to produce such carbonresistance layer in durable corresponding thickness. So-called combresistances were therefore made which carry upon the resistance layermetallic strips arranged in the manner of the teeth of a comb. Thestrips are connected with the lead-in conductors, and the structuretherefore forms in this manner a parallel connection of a plurality oflaminated resistances of high resistance values resulting in a laminatedresistance having the desired low resistance value. So far as thedependency on the frequency is concerned, such resistances operate likethe usual laminated resistances; that is, they have the inductance of astraight conductor, which is still too great to furnish a resistancehaving a substantially phase-free characteristic within the range ofshort and ultra-short waves.

In order to eliminate this inductance, it was proposed to produce theresistance as a bifilar strip bent upon itself in the manner of ahairpin, the two arms of which were by suitable means spaced from eachother by a small gap, for example, by the use of a mica layer. Such aresistance has a small inductance L, due to the small magnetic innerfield which is embraced by the two arms and has a great capacitance Cdue to the large area of the strip and the small gap between the twoarms. This condition is desired for the purpose of obtaining forlow-ohmic resistances a possibly small time constant T, resulting in theequation L T -R-C with small L and great C, nearly in zero. However,this resistance structure is unsuitable for solving the problem, sincethe resistance value of the bifllar strip rises at high frequencies, dueto the current shifting, to a multiple of its direct current value.Small resistance values cannot be obtained in this manner.

It is proposed, in accordance with the invention, to arrange the currentpath, which extends between the terminals of the resistance, in bifilarconcentric manner relative to an intermediate resistance layer whichcorresponds to the desired resistance value.

The various objects and features of the invention will appear from thedetailed description of some embodiments which will presently berendered with reference to the accompanying drawings. In these drawings,

Fig. 1 shows in diagrammatic sectional view an example of a resistancemade in accordance with the invention, the parts including the variouslayers being indicated on a greatly enlarged scale;

Fig. 2 indicates a modification in similar diagrammatic representation;and

Fig. 3 illustrates a detail of Fig. 2 in developed view.

Like parts are indicated by like reference numerals throughout thedrawings. Known details and elements will be referred to only to theextent required for explaining the invention.

The structure shown in Fig. 1 comprises a tubular ceramic member I onwhich is disposed, for example, by spraying, a resistance layer 2. Thelatter may be a mixture containing silver and carbon black. Upon thisresistance layer 2 is disposed a thin lacquer layer 3 of a suitablethickness, the lacquer layer serving as an insulating intermediate layerbetween the resistance layer 2 and a further resistance layer 4, whch isdisposed on the lacquer layer 3, e. g., by spraying. The resistancelayer 4 is connected with the resistance layer 2 by means of themetallic member 5 disposed at one end of the structure. At the oppositeend the resistance layer 2 is conductively connected with a terminal tab6 and the resistance layer 4 is similarly connected with a terminaltab 1. The spacing between these tabs 6 and 1 is determined by thelength of the two resistance layers 2 and 4, i. e., by the resistancevalue thereof. The tabs are insulated from each other by the lacquerlayer 3, the tab 6 forming a terminal for the resistance layer 2 and thetab 1 forming a terminal for the resistance layer 4.

The current path in the above described structure therefore extendsconcentric and bifilar between the two terminals 6 and 7 over the twoserially related resistance layers 2 and 4 which correspond to thedesired resistance value.

The inductance may be made very small by the use of a very thin lacquerlayer 3 resulting in a small inner field, and the capacitance may bemade great by suitably choosing the dielectric constant of the lacquerand by suitably dimensioning of the lacquer layer. It is possible inthis manner to obtain in low-ohmic resistances frequency independencewithin the range of short waves, even in cases where the resistancevalue is smaller than 1 ohm.

Instead of forming both layers 2 and 4 as resistance layers, it ispossible to formonly one such layer as a resistance layer, employing.for the other layer a metallic layer which isa good conductor. Forexample, if the layer 4 is formed as a resistance layer, the layer 2 maybe omitted and a metallic tube, e. g., a brass tube, may be employed asa carrier in place of the ceramic tube I. The current path will thenextend from the terminal 6 over the metallic tube (taking the place ofthe tube l and resistance layer 2), and then over the conductive memberand back tothe terminal 1 over the resistance layer 4 which is.insulated from the metallic tube by a thin lacquer layer 3.

As shown in Fig. 2, the invention may also be applied in connection withthe so-called comb resistances. Thev ceramic tube i is in this caseprovided with a resistance layer 2' which may be sprayed thereon. Thisresistance layer, which appears: in Fig. 3 indeveloped view, carries aplurality of metallic strips and 9 in comblilze rangement, asv is alsoindicated in Fig. 3. Fig. 2

shows two of the strips 8: and 9 insection, the:

strips 8 being interconnected by means of the terminal tab l8, and; thestrips 9. being intercon 116613665. over the metallic member it, forexample, With. a. conductive silver layer l2 which The is interconnectedwith the terminal tab l3. silverlayer l2 is sprayed? on after placing onthe resistance arrangement an insulating lacquer layer It: The currentpath extends in this structure from the terminal tab If! to theindividualconductively interconnected metallic strips 8'. and from thereto the conductivelyinterconneced strips ii over. the intermediateresistance: layer 2" and over the metallic member H and: the silverlayer [2; to the terminal tab- [3.

It; will be seen that the current path between the two: terminalsextends again concentric and bifila-r through the interconnection ofthe31'esistance layer 2 which corresponds to a desired resist.- ance.value.

or" the frequency within therange of short waves.

It may be mentioned, in. conclusion, that a protective-layer ofelectrically. oxidized. aluminum may be. used in place of the insulatinglacquerlayer s-uchas the layer 3- in Fig. 1 or lc-in:Fig..2, and thatsuitable insulating; means may beemrployed which have asuitable-andfavora'ble:di-- electric constant and which canbe appliedin:

very thin layers;

I claim:

having a predetermined resistance value.

The inductance is small. and the capacitance is great,makingthe'structure in the presence-of small resistance value,independent:

2. The structure defined in claim 1, wherein said current path is formedby means comprising a tubular insulating carrier member, a resistancelayer on said insulating member, conductive strips arranged on saidinsulating layer in the manner of the teeth of a comb, first terminalmeans conductively connected with one series of said strips, aconductive layer disposed concentrically with said resistance layer,second terminal means connected with said conductive layer, and aninsulating intermediate layer disposed between said conductive layer andsaid resistance layer.

3. A low-ohmic resistance which has in the range of short waves asubstantially constant, substantially phase-free resistance valuecomprising concentrically disposed current-conducting layers, anintermediate insulating layer between said conducting layers, means forconductively interconnecting said conducting layers at one end thereof,and terminal means for each or said conducting layers disposed at theother end thereof, said terminal means being insulated from each otherand: spaced from each other by a predetermined gap.

4. The structure defined in claim 3,. together with a tubular insulatingcarrier member for said current-conducting. layers.

5. The structure defined in claim 3. wherein a resistance layerconstitutes one of saidcurrent-- conducting layers.

6.. The structure defined in claim 3, whereina resistance layerconstitutes the outer one of said current-conducting layers while a conductiv'e metallic layer' constitutes the inner layers 7 The structuredefined: in claim 3;. whereina resistance layer constitutes the outerone of said current-conducting layers while the inner layer is formed bya metallic tubular carrier member.

8; A low-ohmic resistance: which has: in the range of short waves asubstantially constant. substantially phase-free resistance value com--prising a tubular insulating carrier member; a resistance layeron saidcarrier member; two sets of respectively conductively interconnected'longi tudinally extending metallic strips: disposed on said resistancelayer, an insulating layer on said metallic strips, and-a conductivelayer 011 said insulating layer.

9-.- An electricalresistanceof the class described" comprising meansforming aninsulatingcarrier member, a plurality of conductive layersdisposed on said carrier member, a protective layer of electricallyoxidized aluminum disposed between adjacent conductive layers; means fori'nterco'n meeting said conductive layersat one-end thereof, andterminal means for said-conductive-layer's' at the other end thereof.

ADOBE REFERENCES CIT-ED The following. references are of record in thefile. ofI'this patent:

UNITED STATES PATENTS Number Name nave- 2.lll,7l0 Van Loon Mar. 22, 19382,498,755 Fulmer et al Feb. 28, 1950 2,518,225 Dorst Aug. 8, 1950

